The present invention relates to apparatus and methods for monitoring patient activity, and in particular, to an apparatus and a method which provides notice to attending personnel of the possibility of impending injury to the patient.
Systems have been known heretofore for monitoring the activity of a patient for whom there is a substantial likelihood of injury if the patient is permitted to ambulate without assistance.
One type of such system, as exemplied by U.S. Pat. No. 3,781,843 of Harrison, et al., makes use of fluid-filled sensors attached to the top portions of the side rails and footboard of a bed. An alarm is triggered in response to the displacement of a predetermined volume of fluid which is caused by the patient's grasping the sensors as he attempts to leave the bed. This system suffers from the disadvantage of operational failure and inconvenience due to fluid leaks in the sensors. In addition, such a system would be difficult to adapt for use on the arm rests of a wheelchair to which a patient may be confined.
Another type of system makes use of pneumatic pressure sensors to monitor patient activity. U.S. Pat. No. 4,020,482 of Feldl describes a patient monitor which comprises an elongated air-inflated flexible bag which is placed between the mattress and springs of a bed. The air-inflated bag is operatively connected to a pressure-actuated electrical switch which closes to produce a signal that activates an alarm whenever the weight of the patient is removed, thereby to indicate that the patient is attempting to leave the bed.
U.S. Pat. No. 4,175,263 of Triplett, et al. describes a patient monitor which makes use of two pneumatically inflated pressure sensors. One sensor measures the weight of the patient while he is lying in bed, and the other sensor measures the pressure applied to the guard rails of the bed by the arms of the patient when he is attempting to leave the bed. An alarm is activated in response to the detection of a shift in weight from the first pressure sensor to the second pressure sensor to indicate that the patient is attempting to leave the bed.
The systems described by Feldl and Triplett, et al. suffer from the disadvantage of operational failure due to a reduction in air pressure or air leaks in the sensors. In addition, such systems are not readily adaptable for use in monitoring the activity of a patient confined to a wheelchair or other patient transportation means.
A third type of system, as exemplified by U.S. Pat. No. 3,547,106 of Bornmann, employs an activity detecting system which makes use of a magnet secured to the patient and positioned proximate to a stationary sensing coil to produce an electric signal in response to the changing magnetic field caused by the relative movement between the magnet and the sensing coil. Such a system is reported to be potentially useful for monitoring cyclic movement, such as that produced by the patient's breathing, but would appear to be too sensitive to be responsive only to patient ambulatory movement.
A fourth type of system, as exemplied by U.S. Pat. No. 3,796,208 of Bloice and U.S. Pat. No. 4,196,425 of Williams, Jr., et al., utilizes an electromagnetic wave energy source to produce a field surrounding at least a part of the patient and a detector to measure the disturbance of the electric field caused by movement of the patient. As in the case of the magnetic field sensing system, an elaborate system of this type would appear to be too sensitive to distinguish the attempt of a patient to leave an area of confinement from movement due to normal breathing or mere restlessness of the patient.
The fifth and most common type of patient activity monitoring system makes use of pressure sensitive electric switches which are responsive to the weight of the patient to indicate whether the patient has remained in bed. For example, U.S. Pat. No. 4,263,586 of Nicholas and U.S. Pat. No. 2,425,790 of Fletcher disclose the use of a pressure-operated electric switch which is installed under a leg of a bed to produce a signal in response to the lessening of the weight on the leg when the patient leaves the bed.
U.S. Pat. No. 3,325,799 of Farris and U.S. Pat. No. 2,260,715 of Ketchem describe the use of a pressure-operated electric switch which is installed beneath or within the mattress of the bed.
U.S. Pat. No. 4,067,005 of Levy, et al.; U.S. Pat. No. 3,961,201 of Rosenthal; and U.S. Pat. No. 299,649 of Keep, et al. exemplify the use of electric switches connected to the side rails, headboard, and footboard of the bed to detect the movement of a patient attempting to climb over them.
U.S. Pat. No. 3,991,414 of Moran discloses the use of a mercury switch housed in a cartridge which is mounted on a portion of a bed frame for pivotal movement in response to the deflection of two deflection elements which move in accordance with the shift in weight of a patient who is changing positions on or is departing from the bed. A patient leaving the bed removes his weight therefrom to permit pivotal movement of the mercury switch. Such pivotal movement alters the position of the mercury contained within the switch cartridge so that the mercury comes into contact with the two spaced-apart switch electrodes to close the switch and produce an electric signal indicating that the patient has left the bed.
All of the aforementioned activity monitors of this type suffer from the disadvantage of being permanently attached to the bed and, therefore, are not readily adaptable for use with a wheelchair or other transportation device to which a patient could be confined. The systems are also susceptible to the giving of false alarms, thereby to be unreliable, possibly even creating a nuisance for attending personnel.
An object of this invention, therefore, is to provide an apparatus and a method which produces a definitive indication that a patient has assumed an ambulatory enabling position and thereby may be in imminent danger of injury.
Another object of this invention is to provide such an apparatus and a method which comprehend the sensing of the downwardly directed inclination of the distal end of the femur portion of the patient's leg to indicate that the patient is in an enabling position or is attempting to leave the bed, chair, or gurney he has been occupying.
A further object of this invention is to provide such an apparatus which is portable and is worn by the patient to facilitate continuous monitoring of the patient's activity.
Still another object of this invention is to provide such an apparatus which produces an alarm signal that is indicative of impending patient egress from one of the various types of objects which he might occupy.